Analyses of ancient food webs reveal important paleoecological processes and responses to a range of perturbations throughout Earth's history, such as climate change. These responses can inform our forecasts of future biotic responses to similar perturbations. However, previous analyses of ancient food webs rarely accounted for key differences between modern and ancient community data, particularly selective loss of soft-bodied taxa during fossilization. To consider how fossilization impacts inferences of ancient community structure, we (1) analyzed node-level attributes to identify correlations between ecological roles and fossilization potential and (2) applied selective information loss procedures to food web data for extant systems. We found that selective loss of soft-bodied organisms has predictable effects on the trophic structure of “artificially fossilized” food webs because these organisms occupy unique, consistent food web positions. Fossilized food webs misleadingly appear less stable (i.e., more prone to trophic cascades), with less predation and an overrepresentation of generalist consumers. We also found that ecological differences between soft- and hard-bodied taxa—indicated by distinct positions in modern food webs—are recorded in an early Eocene web, but not in Cambrian webs. This suggests that ecological differences between the groups have existed for ≥48 Myr. Our results indicate that accounting for soft-bodied taxa is vital for accurate depictions of ancient food webs. However, the consistency of information loss trends across the analyzed food webs means it is possible to predict how the selective loss of soft-bodied taxa affects food web metrics, which can permit better modeling of ancient communities.

An increasing number of unexpectedly diverse benthic communities are being reported from microbially precipitated carbonate facies in shallow-marine platform settings after the end-Permian mass extinction. Ostracoda, which was one of the most diverse and abundant metazoan groups during this interval, recorded its greatest diversity and abundance associated with these facies. Previous studies, however, focused mainly on taxonomic diversity and, therefore, left room for discussion of paleoecological significance. Here, we apply a morphometric method (semilandmarks) to investigate morphological variance through time to better understand the ecological consequences of the end-Permian mass extinction and to examine the hypothesis that microbial mats played a key role in ostracod survival. Our results show that taxonomic diversity and morphological disparity were decoupled during the end-Permian extinction and that morphological disparity declined rapidly at the onset of the end-Permian extinction, even though the high diversity of ostracods initially survived in some places. The decoupled changes in taxonomic diversity and morphological disparity suggest that the latter is a more robust proxy for understanding the ecological impact of the extinction event, and the low morphological disparity of ostracod faunas is a consequence of sustained environmental stress or a delayed post-Permian radiation. Furthermore, the similar morphological disparity of ostracods between microbialite and non-microbialite facies indicates that microbial mats most likely represent a taphonomic window rather than a biological refuge during the end-Permian extinction interval.

As the most recent time in Earth history when global temperatures were warmer than at present, the peak of the last interglacial (Marine Isotope Substage [MIS] 5e; ~120,000 years ago) can serve as a pre-anthropogenic baseline for a warmer near-future world. Here we use a new compilation of 22 fossil localities in California that have been reliably dated to MIS 5e to establish baseline expectations for contemporary bivalve species movements by identifying and analyzing bivalve species with “extralimital” ranges, that is, species that occupied the California region during MIS 5e but are now restricted to adjacent regions. We find that 15% of species (n = 142) found in MIS 5e localities have extralimital ranges and currently occupy warmer waters to the south of the California region. The majority of extralimital occurrences occur in paleo-embayments, suggesting that these sheltered habitats were more suitable habitats for warm-water species than exposed coasts during the MIS 5e. We further find that extralimital species now tend to occur in cooler, more seasonally productive coastal waters and to occupy more offshore islands when compared with the broader species pool immediately south of California. These findings suggest that high dispersal potential and preexisting tolerances to environmental conditions similar to California's comparatively cool and seasonally productive environments may have enabled extralimital bivalves to colonize the California region during MIS 5e.

Recent studies have acknowledged the many benefits of including fossils in phylogenetic inference (e.g., reducing long-branch attraction). However, unstable taxa are known to be problematic, as they can reduce either the resolution of the strict consensus or branch support. In this study, we evaluate whether unstable taxa that reduce consensus resolution affect support values, and the extent of such impact, under equal and extended implied weighting. Two sets of analyses were conducted across 30 morphological datasets to evaluate complementary aspects. The first focused on the analytical conditions incrementing the terminal instability, while the second assessed whether pruning wildcards improves support. Changes in support were compared with the “number of nodes collapsed by unstable terminals,” their “distance to the root,” the “proportion of missing data in a dataset,” and the “proportion of sampled characters.” Our results indicate that the proportion of missing entries distributed among closely related taxa (for a given character) might be as detrimental for stability as those distributed among characters (for a given terminal). Unstable terminals that (1) collapse few nodes or (2) are closely located to the root node have more influence on the estimated support values. Weighting characters according to their extra steps while assuming that missing entries contribute to their homoplasy reduced the instability of wildcards. Our results suggest that increasing character sampling and using extended implied weighting decreases the impact of wildcard terminals. This study provides insights for designing future research dealing with unstable terminals, a typical problem of paleontological data.

Lanternfishes currently represent one of the dominant groups of mesopelagic fishes in terms of abundance, biomass, and diversity. Their otolith record dominates pelagic sediments below 200 m in dredges, especially during the entire Neogene. Here we provide an analysis of their diversity and rise to dominance primarily based on their otolith record. The earliest unambiguous fossil myctophids are known based on otoliths from the late Paleocene and early Eocene. During their early evolutionary history, myctophids were likely not adapted to a high oceanic lifestyle but occurred over shelf and upper-slope regions, where they were locally abundant during the middle Eocene. A distinct upscaling in otolith size is observed in the early Oligocene, which also marks their earliest occurrence in bathyal sediments. We interpret this transition to be related to the change from a halothermal deep-ocean circulation to a thermohaline regime and the associated cooling of the deep ocean and rearrangement of nutrient and silica supply. The early Oligocene myctophid size acme shows a remarkable congruence with diatom abundance, the main food resource for the zooplankton and thus for myctophids and whales. The warmer late Oligocene to early middle Miocene period was characterized by an increase in disparity of myctophids but with a reduction in their otolith sizes. A second and persisting secular pulse in myctophid diversity (particularly within the genus Diaphus) and increase in size begins with the “biogenic bloom” in the late Miocene, paralleled with diatom abundance and mysticete gigantism.

Interpreting the impact of climate change on vertebrates in the fossil record can be complicated by the effects of potential biotic drivers on morphological patterns observed in taxa. One promising area where this impact can be assessed is a high-resolution terrestrial record from the Bighorn Basin, Wyoming, that corresponds to the Paleocene–Eocene thermal maximum (PETM), a geologically rapid (~170 kyr) interval of sustained temperature and aridity shifts about 56 Ma. The PETM has been extensively studied, but different lines of research have not yet been brought together to compare the timing of shifts in abiotic drivers that include temperature and aridity proxies and those of biotic drivers, measured through changes in floral and faunal assemblages, to the timing of morphological change within mammalian species lineages. We used a suite of morphometric tools to document morphological changes in molar crown morphology of three lineages of stem erinaceid eulipotyphlans. We then compared the timing of morphological change to that of both abiotic and other biotic records through the PETM. In all three species lineages, we failed to recover any significant changes in tooth crown shape or size within the PETM. These results contrast with those documented previously for lineages of medium-sized mammals, which show significant dwarfing within the PETM. Our results suggest that biotic drivers such as shifts in community composition may have also played an important role in shaping species-level patterns during this dynamic interval in Earth history.

Taxonomic status of several members of the family Naticidae is extremely vague because of its simple shell morphology. Conventional taxonomic classification schemes suggest that most of the morphological characters tend to be homoplastic and exhibit convergence. Such morphological convergence complicates naticid taxonomy and makes it difficult to understand the evolutionary history of this group; several unrelated taxa are often misidentified as naticids, thereby exaggerating the actual diversity of this group. Here, we employ a standard landmark-based approach to understand the pattern of morphological evolution of this family. Ordination methods such as principal components analysis and canonical variate analysis were used to create morphospaces, and disparity was quantified using variance and range. Our results reveal that when naticids are compared with their sister taxon, Ampullinidae, the two families show significant differences in their average shapes, despite their superficial resemblances. Among naticids, although the mean shapes of the individual subfamilies are different, overall, the family Naticidae has displayed extreme morphological conservatism from the Jurassic to the Holocene. Interestingly, this conservatism has been unaffected by taxonomic changes—neither the extinction of the subfamily Gyrodinae nor the appearance of the subfamily Sininae affected this morphological conservatism. Naticids have always shown strong ecological preference toward an infaunal mode of life and strict behavioral selectivity in handling and preying upon infaunal organisms, and this ecological and behavioral conservatism could have enabled them to diversify without undergoing a change in their basic Bauplan.

Marsupial carditids of the subfamily Thecaliinae are characterized by the presence of an “incubatory chamber” in female shells, where the eggs hatch and develop during their first stages. According to recent phylogenetic studies, Thecaliinae are closely related to Carditinae, a group that has a byssal gape. This structure occurs in the same area as the incubatory chamber, and both structures could be evolutionarily related. Using the newest phylogenetic context for the subfamilies, we test whether the incubatory chamber of Thecaliinae is related to characters present in Carditinae. We also provided a more precise definition of the implied structures. Two distinct morphologies for the incubatory chamber are described: one with an exteriorly opened pouch (present in the genera Powellina and Milneria) and the other with a completely internal funicular infold (present in Thecalia). The byssal gape is present in the Cardiobyssata clade (Carditamerinae + (Carditinae + Thecaliinae)), and we discuss whether the incubatory chamber could be the result of an exaptation event, and the possible evolutionary pathways implied. According to the present evidence, we propose a co-optation of the byssal gape into a new function (brooding of larvae) at some point during the transition from the Carditinae to the Thecaliinae lineages, thus determining an exaptation. Adaptative processes probably modified this structure into the incubatory chamber (an external pouch first, and a funicular infold later). We discuss alternative scenarios and implications on phylogenetic studies and the importance of considering non-adaptative evolutionary scenarios in the study of evolutionary narratives.

A short stratigraphic interval near Bulin in western Hunan (China) yields multiple specimens of the ~514-Myr-old oryctocarine trilobite Oryctocarella duyunensis. Size data obtained from these specimens indicate that, from meraspid degree 1 onward, degrees represent successive instars. Meraspid growth persisted until a terminal stage was reached, providing the first example of determinate growth in trilobites and, notably, in an early Cambrian species. The sample contains three varieties of such terminal stages, recognized as holaspids, with 9, 10, or 11 thoracic segments, respectively. During the meraspid phase, growth rates were not constant in this species. The pattern of growth seen in the Bulin assemblage differs modestly from that reported in the same species from two other localities, attesting to microevolutionary variation in developmental patterns among these collections.

Cervids living in high latitudes have evolved to thrive in ecosystems that experience dramatic seasonal changes. Understanding these seasonal adaptations is important for reconstructing cervid life histories, ecosystem dynamics, and responses in the distant and not-so-distant past to changing seasonality caused by climate change. Cervid antlers provide a rare opportunity for insight into faunal seasonal ecology, as they are grown and shed each year. Stable isotopes of carbon and nitrogen measured directly from antlers have the potential to provide seasonal dietary data for individuals. If the isotopic signals in bone and antler are controlled by the same metabolic processes, then the stable carbon and nitrogen isotope compositions of collagen (δ13CColl and δ15NColl) from incrementally grown antler tissue provide time-constrained dietary signals from the spring and summer growth season. Bone, by comparison, provides an average signal over several years. The amino acid (glutamate and phenylalanine) δ15N in antlers from modern captive caribou showed similar trophic discrimination factors to earlier results for other collagenous tissues (bone, tooth dentin, and cementum). Hence, growth rate was not the primary control on the stable isotope composition of antler collagen. We applied this knowledge to assess seasonal shifts in Quaternary fossils of three Cervidae species: elk (Cervus elaphus), moose (Alces alces), and caribou (Rangifer tarandus). Paired antler–bone δ13CColl and δ15NColl from the same individual were used to identify differences between summer and annual diet and ecology. Intra-antler isotopic variability from serially sampled antlers was used to examine seasonal dietary shifts and specialization.